This Brain pop is on the ph scale it explains that numbers 1-6 are acids or acidic and 8-14 are bases or alkalines, and number 7 is neutral.

When you dip a ph film into a acid the film will turn some tint of red, and when you dip a ph film into a base the film will turn some tint of blue. Then you match up the color of the film with the closest color on ph scale to find out what number it is.